article: In the days when an ice cream sundae cost much less, a 10-year-old boy entered a hotel coffee shop and sat at a table. A waitress (woman assistant) put a glass of water in front of him. "How much is an ice cream sundae?" "Fifty cents", replied the waitress. The little boy pulled his hand out of his pocket and studied a number of coins in it. "How much is a dish of _ ice cream?" he asked. Some people were now waiting for a table and the waitress was a bit worried. "Thirty-five cents," she said rudely(not politely). The little boy again counted the coins. "I'll have the plain ice cream," he said. The waitress brought the ice cream, put the bill on the table and walked away. The boy finished the ice cream, paid the bill at the counter and went out. When the waitress came back, she began cleaning the table and then she couldn't believe what she had seen. There, placed nearly beside the empty dish, were two five-cent coins and five one-cent coins---her tip .
question: An ice cream sundae was  _  a dish of plain ice cream.
options: fifteen cents cheaper than fifteen cents dearer than fifty cents dearer than as expensive as